A large number of studies has implicated vestibular system dysfunction in the pathophysiology of schizophrenia. The data are ambiguous, however, regarding the specific nature of the pathology and its localization as a peripheral or central finding. In addition to caloric nystagmus dysrhythmia, some schizophrenic and non-schizophrenic psychotic patients show a variety of other oculomotor abnormalities involving slow eye movements, such as smooth pursuit, that are known to accompany central nervous system disturbances. Using a battery of tests of vestibular-oculomotor function and specific measures with localizing value (e.g., failure of fixation suppression of nystagmus), biologically homogeneous subgroups of psychiatric patients will be identified on the basis of clusters of positive CNS signs. The proposed research will also attempt to determine whether these deficits share a common neurophysiological substrate.